The present invention relates to the monitoring of stereo audio signals associated with TV video signals.
In broadcasting generally, and in television broadcasting in particular, the provision of stereo sound is becoming commonplace. This poses special problems in the production and monitoring of TV programmes. It is difficult to monitor sound quality adequately by ear, particularly under production conditions, and some form of instrumentation which gives an indication of sound amplitude and phase is desirable. In particular, it is desirable to be able to monitor the relationship between the two channels of a stereo audio signal.
A well-known technique for doing this is to provide a separate monitor consisting of a conventional oscilloscope which has the two channels of the stereo signal fed to its X and Y inputs respectively; the resulting display is a Lissajou figure. However, this arrangement has the disadvantage that it is separate from the display of the associated TV picture on a TV monitor. The operator therefore has to make an active effort to check the oscilloscope, and there is also ample opportunity for error in associating the oscilloscope display with the appropriate one of a large number of monitors in a typical array of TV monitors.
A stereo audio monitor has also been developed which uses a TV-type picture raster display instead of an oscilloscope vector-type display, with the Lissajou figure being synthesized from the two audio signals as a TV-type video signal. This, however, suffers from the same disadvantages as the oscilloscope display.